#div/0!

Need help! I have three separate formula's that I am using in three separate cells. The first 2 are rounding down to whole # and averaging w/o calculating zero's or empty cells. The third is a simple average to ratio. The question I have is in all three cells I am getting a #DIV/0! error. I found a formula you can use to silence that error but I can't figure out how to use it in conjunction with my existing formula's. Any ideas? The formula's I am using are listed below:

=ROUNDDOWN(AVERAGEIF(B16:CB30,"<>0"),0)
=ROUNDDOWN(AVERAGEIF(C16:C30,"<>0"),0)
=IF(B31=0,"",B31&":"&C31)


Thank you!

Thanks to you both, that worked beautifully! Brilliant.